This invention relates to the production of communiuted products such as fibrous thermal insulation and especially to an improved method and apparatus for producing such products. More particularly, the invention relates to a novel method and apparatus that utilize the energy generated by producing a high velocity flow of air with feed stock entrained therein, combined with mechanical action to comminute the material with minimal damage to the resulting product. This invention relates to and is an improvement on my invention described in my U.S. Pat. No. 4,919,340, and that patent is incorporated by reference herein.
Typically, dry-process comminuting of both organic and inorganic material for use as thermal insulation, absorbent pads, filters, and the like, is achieved by using conventional hammer mills. It has been found, however, that the use of hammer mills cannot produce a comminuted mass optimum physical properties of low mass density, high thermal resistance to heat flow, high moisture absorbance, acceptable aesthetic appearance and other desirable characteristics.
Hammer mill designs utilize hammers or beaters that are pivotally mounted on a series of disks that rotate within a partial cylindrical sizing screen. The feed stock is typically fed into the mill via an air stream flowing perpendicular to the rotating hammers. The entire mass of feed stock is then drawn into a wedge-shaped space and onto the beginning of the sizing screen comprising a major pinch point and then forced through and over a typical semi-cylindrical screen.
Due to the extraordinary pressure exerted on the screen at the entry pinch point, heavy gauge 3/16 to 1/4 inch thick perforated metal screens are needed to prevent breakage from fatigue the heavy gauge further limits the perforated open area to 30 to 40% and restricts the possible use of smaller perforations.
As a result of the input feed method, the swing hammers will retract as the feed stock is worked through the screen, thereby reducing the air flow due to a relatively thick mat of material, blinding the screen and increasing the feed residence time within the machine, resulting in fines and dust. This deficiency is often mitigated by using screens with larger perforations. This results in large, uncomminuted pieces remaining in the product.
Another deficiency is that the hammers are supported between disks, which in turn prevent complete utilization of the comminuting screen surfaces, adding to the blinding of the perforations. As most of the systems are set up to be air swept, blinding of perforations can have a major negative effect by retarding air flow and increasing energy consumption and product degradation.
The method and apparatus of the present invention, however, resolve many of the problems listed above and provide other features and advantages heretofore not obtainable.